This invention relates to a process for cross lapping a fibrous web to produce a batt composed of a plurality of web layers or folds. It is more particularly concerned with improvements in the cross-lapping operation to regulate the basis weight profile of batt cross sections and provide uniform basis weight profiles along any section taken lengthwise of the batt.
Webs of natural fibers or synthetic staple fibers are commonly produced by carding or air-laydown of the fibers. Heavier basis weight batts for cushioning purposes or thermal insulation, e.g., for use in pillows, quilts, garments, sleeping bags, cushions, mattresses or upholstered furniture, are commonly produced by cross-lapping webs to build up the required basis weight. Kalwaites U.S. Pat. No. 3,222,730 discloses carding fibers to form a web which is then deposited in a plurality of overlapping folds on a horizontal receiving conveyor by a "camel-back" cross lapper to form a batt. The cross lapper swings back and forth like a pendulum to guide the web downward onto the conveyor. The web is supported during its downward movement on an oscillating conveyor having a pile fabric surface to reduce slipping of the web. Laydown rolls lap the web onto the horizontal conveyor, which has a porous surface, and suction is applied through the conveyor to hold the laps in place.
Burger U.S. Pat. No. 3,682,734 discloses an improvement over the "camel-back" type of cross lapper apparatus for use in bias crosslaying fiber webs. Web laydown rolls are mounted in carriages arranged to reciprocate horizontally back and forth above a horizontal carrier sheet moving at right angles to the direction of carriage movement. Horizontal belts are mounted in the carriages to support the webs and guide them down around the laydown rolls. Two webs may be crosslaid simultaneously at a spacing which provides crosslayers in edge-to-edge relationship on the carrier sheet, and an additional web may be deposited on top in longitudinal relationship to the carrier sheet. The web composite may be bonded together to produce a laminated structure. In order to provide a composite web having uniform characteristics the edges of the composite web are trimmed off.
Zafiroglu U.S. Pat. No. 3,797,074 discloses an air-laydown process for making uniform webs for producing nonwoven fabrics. However, cross lapping these webs by previously known processes has not provided product uniformity. The improved cross lapping process of the present invention provides means for compensating for process deficiencies which cause nonuniform products. The process provides for modification of cross-sectional basis weight profiles without loss of uniformity along any section taken lengthwise of the batt. For example, a gradual increase in basis weight from the side portions of the batt to the central portion of the batt is readily accomplished. Such batts would be useful in pillows.